©
National Instruments Corp.
19
NI 9214 Operating Instructions and Specifications
Compensating for OTD Current
The OTD c
u
rrent ca
u
ses a voltage error on the inp
u
t when p
u
shing
against a so
u
rce resistance. This error is minimal for many
applications, b
u
t can be significant for some applications that
req
u
ire high acc
u
racy and
u
se long, narrow ga
u
ge thermoco
u
ple
wires that ca
u
se large so
u
rce resistances. Refer to the
section for more information abo
u
t the OTD bias
c
u
rrent.
Yo
u
can also eliminate the OTD bias c
u
rrent by disabling the OTD.
Refer to the software help for information abo
u
t config
u
ring the
OTD circ
u
it. Visit
ni.com/info
and enter
c
s
erie
s
doc
for
information abo
u
t C Series doc
u
mentation.
Yo
u
can compensate for the OTD bias c
u
rrent if yo
u
r application
req
u
ires high acc
u
racy, high resistance thermoco
u
ple wires, and
the ability to detect open thermoco
u
ples. Take a meas
u
rement with
the OTD enabled and a second meas
u
rement with the OTD
disabled. The voltage difference between the meas
u
rements is
the error voltage d
u
e to the OTD bias c
u
rrent. S
u
btract the error
voltage from s
u
bseq
u
ent meas
u
rements.
Visit
ni.com/info
and enter
9214OTD
for more information
abo
u
t compensating for the OTD errors.
NI_9214.fm Page 19 Monday, November 1, 2010 9:52 AM
